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Tuyển tập các báo cáo nghiên cứu về lâm nghiệp được đăng trên tạp chí lâm nghiệp quốc tế đề tài: "Water relations of European silver fir (Abies alba Mill) in 2 natural stands in the French Alps subject to contrasting climatic conditions. | Ann Sci For 1994 51 599-611 Elsevier INRA 599 Original article Water relations of European silver fir Abies alba Mill in 2 natural stands in the French Alps subject to contrasting climatic conditions p Guicherd Université Joseph-Fourier Centre de Biologie Alpine BP 53 38041 Grenoble cedex 9 France Received 30 November 1992 accepted 26 January 1994 Summary This paper reports on the diurnal and seasonal variations in water potential stomatai conductance and transpiration of twigs from silver fir in a mesohygrophilic stand of the external French Alps and in a mesoxerophilic stand in the inner French Alps where this fir grows near its ecological limits. In both stands predawn needle water potential was always 0.2-0.4 MPa below the potential of the driest soil layer. In the first one it was maintained at about -0.4 MPa. Maximum stomatai conductance and maximum transpiration which could reach 200 mmol m2 s and 1 mmol m2 s respectively occurred at the same time which corresponded to minimum leaf water potential. In the dry stand predawn needle water potential never dropped below -1.14 MPa yet a general browning of older needles was already observed. The decrease of predawn needle water potential was accompanied by the decrease of maximum stomatai conductance and transpiration to 15 of their highest value which reached 150 mmol m2 s and 1 mmol m2 s respectively at this stand. Maximum stomatai conductance occurred in general before UT 07.00 and maximum transpiration 5-6 h later irrespective of predawn needle water potential. Furthermore in both stands stomata closed at vapor pressure deficit value as low as 0.3 kPa. This extremely early reaction to water stress exhibited by European silver fir is consistent with its well-known sensitivity to atmospheric humidity and soil water availability. It indicates a strong avoidance strategy which we have hitherto attributed only to species better adapted to drought. Abies alba Mill European silver fir Alps stomata water potential .
